An external drive to backup to – creating a Fusion volume will erase both the SSD and the hard drive, so if you have information on the hard drive you want to keep, you’ll need to have a copy of that data elsewhere. This is optional and if you are just setting up your mac you wouldn’t be needing an extra drive to backup to.

An SSD installed/to install. It is possible to build a Fusion Drive through an internal or externally connectedd SSD. Though the recommended method is using an internal drive because if you accidentally remove the SSD – the Fusion Drive would not function and will crash. In this tutorial we will be looking at building a Fusion Drive through an internally connected SSD. Nonetheless, the process and commands are the same for an externally connected SSD, so you can always follow these steps.

1. Organise Your Drives

We need to two drives for a Fusion Drive. In this tutorial we will look at the Hitachi 1TB 2.5-inch hard drive (the one that ships in a Mac mini) and the 240GB OWC Mercury Extreme Pro 6G SSD.

Apple chooses the drives based on extensive testing which is the reason why they do not recommend creating your own Fusion Drives.

2. Clone Your Data

If you have any data that you would like to keep from any of these two drives, this is the time to back it up. The process (CoreStorage) to build a Fusion Drive will erase all data from the drives.

Have a look at ourfoolproof guide for creating a backup system for your Macif you need help with backing up.

3. Start Up Terminal

The Disk utility application that comes with every OS X does not support the creation of Fusion Drives. Though we will be using the Disk utility , we will be looking at the command line version of the application that has more features.

A list of Disk Utility’s CoreStorage Terminal commands

You can’t boot into a drive you want to use as part of the fusion drive if that’s the case then you will need to go into recovery mode and use terminal from there. The CoreStorage process that is used to “fuse” the drives also will format them and you can’t do that to a drive you are booted to.

Boot into recovery mode by clicking and holding command+R, immediately after the start-ip chime, when starting up your Mac.

4. Lets Build it!

Now that we have terminal open and our booted into recovery mode, we can start building the drive.

List the drivesyour system can see by entering the following command:

diskutil list

This will list the drives for you to see like this:

A list of attached devices using the command “diskutil list”

The drive mounts are labelled as /dev/disk# . Note down the drives you want to fuse.

In my mac /dev/disk0 is the boot disk and /dev/disk1 & /dev/disk2 are the drives that I will fuse. An easy way to tell which is the SSD and which is the Hard drive is by the sizes indicated. Make sure you dont confuse the names as there isn’t a warning before terminal will erase them forever.

Create a logical Volume Group.Now lets create a CoreStorage Logical Volume Group that will have the pool that we will use as the Storage space for our drive.To do this use the following command:

diskutil coreStorage create nameYourThing drive1 drive2

Now combine the drives/dev/disk1 ir /dev/disk2by typing:

diskutil coreStorage create myLogicalVolGroup /dev/disk1 /dev/disk2

When the process is complete your Logical Volume Group should have been successfully completed and Terminal will present you with a Unique Identifier for the group which should look like this. You should also copy this to your clipboard.

The UUID is the unique identifier you want to copy

Create the Logical Volume.Now that we have the Logical Volume Group, we can create the logical volume that the Mac will recognize as a Single Drive.Type the following command to create the logical Volume:

diskutil coreStorage createVolume lvgUUID type name size

lvgUUIDis the unique identifier you copied from the previous step.

typeuse Journaled HFS+ (typed asjhfs+).

namecan be whatever you want to name the drive (traditionally “Macintosh HD” is used and I recommend it as its the name used in many other tutorials online). Make sure you use quotes if there’s a space in the name.

sizeis how much of the “pool” that you want to make into a drive, using the following suffixes: B(ytes), S(512-byte-blocks), K(ilobytes), M(egabytes), G(igabytes), T(erabytes), P(etabytes), arba (%) a percentage of the current size of the logical volume group.